The present invention relates generally to the field of servo control systems. More particularly, the present invention relates to self-writing servo patterns within a storage device.
Various conventional techniques exist for writing servo data to storage device media, e.g., hard drive disk surfaces. One conventional approach to servo writing involves writing an entire servo pattern on a disk outside of a disk drive, where the writing is done on a servo track writer with write heads/circuitry and other disk drive electronics. The disk can then be installed in the disk drive. Another conventional approach, referred to as servo track writer-assisted servo writing, comprises installing unwritten disks in a disk drive, after which a servo track writer uses a clock head and pushpin actuator to assist the disk drive head/electronics to lay down an entire servo pattern. Yet another conventional method of servo writing can be referred to as servo track writer-assisted reference pattern writing, where unwritten disks are installed in a disk drive and a servo track writer assists the disk drive head/electronics in writing a spiral reference track. Thereafter, the disk drive completes the actual servo pattern writing in a test rack without the use of the servo track writer. In a variation of reference pattern writing, reference spirals can be written on a disk before the disk is installed in the disk drive on a servo track writer with write heads and electronics. Once the reference spirals have been laid down on the disk, the disk is installed in the disk drive and the disk drive itself completes the actual servo pattern writing in a test track, again without the servo track writer. Alternatively, servo track writing can be accomplished without the use of a servo track writer, where unwritten disks are installed in a disk drive and the disk drive writes its own spiral reference pattern based on a disk locked clock. Utilizing the fine control of a voice coil motor (VCM) implemented within the disk drive, the VCM can use the spiral reference pattern to write the remaining servo pattern.
However these processes are time consuming and cost intensive.
In addition, such conventional servo writing techniques use a high precision micro positioner (i.e., push-pin actuator) on the servo track writer. Depending on the number of reference spirals (i.e., reference pattern) being laid down, and the speed being used during the spiral write, there is a certain amount of process time imparted by the servo track writer. This process time becomes longer with higher tracks per inch (TPI) and higher sampling rate disks. A high process time leads to a high cost of equipment, as many systems are required to operate in parallel. Hence, writing reference spirals utilizing only a VCM, thereby removing the dependency on push-pin actuators and achieving significant equipment cost reduction is desirable.
The conventional servo writing approaches also require a longer velocity ramp up length (i.e., the stroke needed to ramp up speed) before a desired spiral velocity is reached, where the velocity ramp up length is limited by hardware (i.e., microE positioner). This translates to a loss of usable disk space and implies that a higher TPI is needed to retain a desired capacity design point. This could potentially prohibit the use of spiral servo writing technology on smaller form factor disk drives.
Lastly, although certain reference pattern write processes can be accomplished in part by utilizing a VCM, it would be desirable to control VCM motion in a radial direction in a precise and repeatable manner, so that reference spirals written onto the media (i.e., disk surface) would have satisfactory spacing accuracy, provided that tangential timing, spindle, or disk angular speed control is adequately accurate. However, it would be desirable to control VCM motion to achieve desired spiral velocity with satisfactory accuracy and repeatability over the entire media surface without servo track position information.